The present invention relates to acoustics. More particularly, it relates to an ultrasonic system and method incorporating a ceramic horn for long-term delivery of ultrasonic energy in harsh environments, such as high temperature and/or corrosive environments.
Ultrasonic is the science of the effects of sound vibrations beyond the limit of audible frequencies. The object of high-powered ultrasonic applications is to bring about some physical change in the material being treated. This process requires the flow of vibratory energy per unit of area or volume. Depending upon the application, the resulting power density may range from less than a watt to thousands of watts per square centimeter. In this regard, ultrasonics is used in a wide variety of applications, such as welding or cutting of materials.
Regardless of the specific application, the ultrasonic device or system itself generally consists of a transducer, a booster, a waveguide, and a horn. These components are often times referred to in combination as a “horn stack”. The transducer converts electrical energy delivered by a power supply into high frequency mechanical vibration. The booster amplifies or adjusts the vibrational output from the transducer. The waveguide transfers the amplified vibration from the booster to the horn, and provides an appropriate surface for mounting of the horn. Notably, the waveguide component is normally employed for design purposes to reduce heat transfer to the transducer and to optimize performance of the horn stack in terms of acoustics and handling. However, the waveguide is not a required component and is not always employed. Instead, the horn is often times directly connected to the booster.
The horn is an acoustical tool usually having a length of a multiple of one-half of the horn material wavelength and is normally comprised, for example, of aluminum, titanium, or steel that transfers the mechanical vibratory energy to the desired application point. Horn displacement or amplitude is the peak-to-peak movement of the horn face. The ratio of horn output amplitude to the horn input amplitude is termed “gain”. Gain is a function of the ratio of the mass of the horn at the vibration input and output sections. Generally, in horns, the direction of amplitude at the face of the horn is coincident with the direction of the applied mechanical vibrations.
Depending upon the particular application, the horn can assume a variety of shapes, including simple cylindrical, spool, bell, block, bar, etc. Further, the leading portion (or “tip”) of the horn can have a size and/or shape differing form a remainder of the horn body. In certain configurations, the horn tip can be a replaceable component. As used throughout this specification, the term “horn” is inclusive of both uniformly shaped horns as well as horn structures that define an identifiable horn tip. Finally, for certain applications such as ultrasonic cutting and welding, an additional anvil component is provided. Regardless, however, ultrasonic horn configuration and material composition is relatively standard.
For most ultrasonic applications, accepted horn materials of aluminum, titanium, and steel are highly viable, with the primary material selection criteria being the desired operational frequency. The material to which the ultrasonic energy is applied is at room temperature and relatively inert, such that horn wear, if any, is minimal. However, with certain other ultrasonic applications, wear concerns may arise. In particular, where the horn operates in an intense environment (e.g., corrosive and/or high temperature), accepted horn materials may not provide acceptable results. For example, ultrasonic energy is commonly employed to effectuate infiltration of a fluid medium into a working part. Fabrication of fiber reinforced metal matrix composite wires are one such example whereby a tow of fibers are immersed in a molten metal (e.g., aluminum-based molten metal). Acoustic waves are introduced into the molten metal (via an ultrasonic horn immersed therein), causing the molten metal to infiltrate the fiber tow, thus producing the metal matrix composite wire. The molten aluminum represents an extremely harsh environment, as it is both intensely hot (on the order of 700° C.) and chemically corrosive. Under severe conditions, titanium and steel horns will quickly deteriorate. Other available metal-based horn constructions provide only nominal horn working life improvements. For example, metal matrix composite wire manufacturers commonly employ a series of niobium-molybdenum alloys (e.g., at least 4.5% molybdenum) for the horn. Even with this more rigorous material selection, niobium-based horns provide a limited working life in molten aluminum before re-machining is required. Moreover, near the end of their “first” life, niobium alloy horns become unstable, potentially creating unexpected processing problems. In addition, formation of the niobium-molybdenum alloy horns entails precise, lengthy and expensive casting, hot working, and final machining operations. In view of the high cost of these and other materials, niobium (and its alloys) and other accepted horn materials are less than optimal for harsh environment ultrasonic applications.
Ultrasonic devices are beneficially used in a number of applications. For certain implementations, however, the intense environment in which the ultrasonic horn operates renders current horn materials economically unavailing. Therefore, a need exists for an ultrasonic energy system, and in particular an ultrasonic horn, adapted to provide long-term performance under extreme operating conditions.